update socket protocol to get version string

Add a new method to get the version data from the fail2ban socket and
return it to the metric collector. The version is now correctly exposed.

src/exporter.go

@@ -282,9 +282,14 @@ func (e *Exporter) collectJailStatsMetric(ch chan<- prometheus.Metric, s *socket
 }
 
 func (e *Exporter) collectVersionMetric(ch chan<- prometheus.Metric, s *socket.Fail2BanSocket) {
-	fail2banVersion := "9.9.9"
+	var err error
+	var fail2banVersion = ""
 	if s != nil {
-		// TODO: Get fail2ban server version
+		fail2banVersion, err = s.GetServerVersion()
+		if err != nil {
+			e.socketRequestErrorCount++
+			log.Printf("failed to get fail2ban server version: %v", err)
+		}
 	}
 
 	ch <- prometheus.MustNewConstMetric(

src/socket/fail2banSocket.go

@@ -118,6 +118,20 @@ func (s *Fail2BanSocket) GetJailStats(jail string) (JailStats, error) {
 	return stats, newBadFormatError(statusCommand, response)
 }
 
+func (s *Fail2BanSocket) GetServerVersion() (string, error) {
+	response, err := s.sendCommand([]string{versionCommand})
+	if err != nil {
+		return "", err
+	}
+
+	if lvl1, ok := response.(*types.Tuple); ok {
+		if versionStr, ok := lvl1.Get(1).(string); ok {
+			return versionStr, nil
+		}
+	}
+	return "", newBadFormatError(versionCommand, response)
+}
+
 func newBadFormatError(command string, data interface{}) error {
 	return fmt.Errorf("(%s) unexpected response format - cannot parse: %v", command, data)
 }

src/socket/protocol.go

@@ -11,6 +11,7 @@ const (
 	commandTerminator    = "<F2B_END_COMMAND>"
 	pingCommand          = "ping"
 	statusCommand        = "status"
+	versionCommand       = "version"
 	socketReadBufferSize = 1024
 )